Progress in microfabrication techniques applied in recent semiconductor manufacturing processes has been accompanied by higher integration of circuits incorporated in integrated circuit devices. However, there has been little technological advance with regard to the spacing of I/O (input/output) pads of the chip. As a consequence, the area occupied by the I/O portions is large and this has become a major obstacle to higher integration of integrated circuit devices.
Accordingly, in recent years an integrated circuit device has been developed in which chips on which electromagnetic induction coils have been formed are stacked vertically and signal transmission is performed using opposing electromagnetic induction coils between chips (see Patent Documents 1 to 3). FIG. 21A is a planar projection of a conventional integrated circuit device in which signal transmission is performed using electromagnetic induction coils, and FIG. 21B is a sectional view thereof. This integrated circuit device is obtained by stacking chips 6 in the vertical direction and securing the chips to each other by an adhesive layer 7. Formed on the opposing faces of the chips 6 are respective conductor patterns 1 that operate as electromagnetic induction coils, and signal devices 3 that receive a current signal generated in the respective coil or that supply a current signal to the coil.
The device will be described assuming that the coil and signal device placed on the upper chip are for transmission and the coil and signal device placed on the lower chip are for reception. Current is supplied to the transmitting coil from the signal device in a direction that depends upon the transmit signal. For example, if we let “1” be a current signal in the clockwise direction as seen from the top surface of the chip, then the transmitting coil generates a magnetic flux in a direction that penetrates through the receiving coil from the top down. An induced current flows into the receiving coil owing to the magnetic flux that has penetrated through the interior of the coil. At this time the direction of the induced current is the same as the direction of the current supplied to the transmitting coil. By using the signal device to measure the induced current produced or an electric signal such as a voltage obtained by conversion, signal transmission is completed.
If it is desired to transmit a “0” signal, then a current is supplied to the transmitting coil in the counter-clockwise direction, which is opposite the direction in the case of “1”, thereby making it possible to transmit the “0” signal.
In general, a signal transmission system using the electromagnetic coupling of electromagnetic induction coils is such that the area occupied by the I/O portions is smaller that of a packaging system using area bumps, thus making it possible to raise the packing density of integrated circuits.                [Patent Document 1] Japanese Patent Application Laid-Open No. 7-221260        [Patent Document 2] Japanese Patent Application Laid-Open No. 8-236696        [Patent Document 1] Japanese Patent Application Laid-Open No. 10-200007        